Herb and BG are right,but if you don't have $200 for a vacuum and refill,or hundreds more for a proper repair,there is a fairly safe alternative.The add a can kit at the auto parts will usually bring the AC back to life.First,with the air on,ck that the pusher fan is running,then watch the compressor to see if it cycling rapidly.Feel the accumulator(shiny can near firewall) to see if it is cold,cool or warm.

If the compressor is cycling fast,the can is just cool or warm,it is safe to add a can.Follow all the safety info and instructions on the kit.Buy the fit with the built-in pressure gauge.

Bill